How Many Watts to Keep My Laptop Charged

@Hudd19  sorry, I got so deep into that explanation above that I forgot you were asking about a USB-C display.  If you're looking at a Dell USB-C display that provides up to 90W, then since you've already confirmed that the system you have supports USB-C charging, it should draw the full 90W as long as you use it with an appropriate cable such as the one that comes with the display -- but as I said above, if you have a system designed for 130W, then you might not get optimal performance when you're using a power source that's only 70% of what the system is supposed to have.  And if you're looking at a non-Dell display, then you'd likely be limited to 65W max, which is only HALF what the system is supposed to have.  To my knowledge, Dell doesn't have any current displays that provide 130W.

@Hudd19  The wattage of the power adapter that Dell ships with a laptop is the amount of power it is designed to have available.  In many cases, you can use power sources with lower wattage (down to a point), but if you use an undersized power source, the system might have to take steps to reduce its power consumption in order to work within that reduced power budget.  So for example you might experience slower battery charging, reduced CPU and/or GPU performance, and in extreme workload cases the system might continue to drain the battery in order to make up the shortfall, although that's a last resort because that is not a "sustainable" operating model, i.e. in that case your system could eventually die even while it's connected to a power source.

As a frame of reference, the XPS 15 models are also designed for a 130W power source, but they will use power sources as low as 60W.  I don't think they'll even bother trying to use anything lower than that.  However, people who have actually used a 60W power source have found that both the battery charging speed and normal performance of their XPS 15 drops significantly when that power source is connected.  The system is actually faster running on battery power -- again, because while connected to a power source the system assumes that you would prefer that it operate "sustainably", even at lower performance, rather than maintaining maximum performance and therefore having to continue draining its battery even while connected to power.  Some people are still fine using a 60W charger as a travel charger because they like that 60W chargers are small and they only plan to use that charger for overnight charging when their system isn't running, in which case they don't have to worry about slow charging or reduced performance -- but if you want to use a charger while the system is running, you might not be happy with the results.

In addition to all of that, to my knowledge, all Dell laptops as of this writing limit themselves to drawing no more than 65W over USB-C from non-Dell power sources, even when the power source can provide more and the system would benefit from more.  I don't know why Dell has this limitation, but I've observed this myself on multiple Dell systems, as have others.  I even wrote up this thread about it.  I have a 90W Nekteck USB-C charger that is used as a 90W source with a non-Dell laptop I have, but the XPS 15 limits itself to 65W when used with that same charger (and cable).

As it happens, Dell actually offers a 130W USB-C charger, which they originally created for the XPS 15 2-in-1 9575, since that system doesn't have a "conventional" AC adapter connector.  That's actually above the 100W maximum of the official USB PD spec, so Dell did something proprietary there.  Some Dell docks also support providing 130W over USB-C/TB3, specifically to support systems like the XPS 15.  That said, I don't know if the Inspiron system you have would accept 130W over USB-C even from Dell's official charger, and unfortunately Dell's 130W USB-C charger isn't a great option for other use cases because it only supports 5V and 20V output, which means it won't be usable as a fast charger for devices that only allow fast charging at 9V and 15V.

So if you're only concerned about getting a charger for that system, I would consider either Dell's 130W USB-C charger to see if the system uses it at 130W, or else getting a third-party 65W USB-C charger since that's all the system will use anyway.  Or you might want to get a higher wattage charger just to support other devices you have or may purchase later.  There are some 100W USB-C chargers that are surprisingly small because they use a relatively new technology called gallium nitride (abbreviated GaN) that allows them to be smaller -- but they're a bit more expensive.  Also note that in order to exceed 60W, you need a USB-C cable rated for up to 100W.  Most USB-C cables are only rated for up to 60W, and if you use that type of cable, then that's all you'll get even if both your charger and device would otherwise provide/use more.  On many Dell systems, if you go into the BIOS and look under the "Battery information" section, underneath the battery graphic, the system will identify the wattage of the attached power source.  With a conventional Dell power source (non-USB-C), it will be the true wattage of the power source.  With USB-C, it will be either the max wattage of the power source or the max wattage the system will draw from it, whichever is lower.  For the latter, that will either be 65W based on the third-party limitation I just described, or possibly even lower if the system doesn't require that much.  An XPS 13 is designed for 45W for example, so it will never show a figure higher than that for a USB-C source.

Hopefully this helps.